(401ai) Cross-Linked Polyimides for Membrane H2/CO2 Separation at Elevated Temperatures
Maryam Omidvar, Mark Swihart, and Haiqing Lin
Department of Chemical and Biological Engineering
University at Buffalo, The State University of New York)
Membrane technology has attracted significant interests for H2 purification and CO2 capture in the pre-combustion processes. The key to the success of this technology is membrane materials with high H2 permeability and H2/CO2 selectivity at elevated temperatures of syngas processing such as 100 °C or above. Polyimides such as P84 have been explored for H2/CO2 separation due to their strong size-sieving ability and thus high H2/CO2 diffusivity selectivity. In this study, we demonstrate that these polymers can be cross-linked chemically to further improve the size sieving ability and thus H2/CO2 selectivity. We systematically evaluate the effect of the cross-linking in P84 using amines such as propane diamines, butane diamines and p-xylene diamine on the H2/CO2 separation properties. The cross-linking can significantly increase H2/CO2 selectivity while retaining moderate H2 permeability.Â For example, cross-linking of P84 with butane diamine with 42% conversion rate increases H2/CO2 selectivity from 2.4 to 8.0, while decreasing H2 permeability from 40 to 24 Barrers at 100 oC. The properties of 24 Barrers for H2 permeability and 8.0 for H2/CO2 selectivity are very close to the Robesonâs upper bound for H2/CO2 separation, demonstrating the potential of this approach for membrane development. These cross-linked polymers are thoroughly evaluated using FTIR, DSC, TGA, WAXD, and XPS. The effect of cross-linking degree on the physical properties will be discussed, including glass transition temperature, fractional free volume and pure- and mixed-gas H2/CO2 separation properties at various temperatures. This presentation will also discuss the fundamental structure/property relationship in these highly cross-linked polymers with promising H2/CO2 separation properties.